As a transistor for a semiconductor device, a silicon transistor is mainly used. However, for the manufacturing process of the silicon transistor, a large-scale facility, such as a clean room, is required. Also, complicated processes, including doping of p-type (or n-type) impurities into a silicon substrate, and photolithography, are required.
Accordingly, the development of an organic transistor using an organic-based semiconductor layer has been recently considered. In the fabrication process of an organic transistor, since a thin film layer can be formed by a coating film, a printing process, such as inkjet, may be used. Thus, the fabrication process of the organic transistor may be simple, and thus reduce a manufacturing cost, compared to that of a silicon transistor. Also, there is another advantage in that a flexible plastic substrate may be used as a substrate. Meanwhile, the organic transistor has a problem in that carrier mobility of organic molecules is lower than that of silicon single crystals. However, research on this problem is smoothly being conducted through the development of materials.
For example, Japanese Patent Laid-Open Publication No. 2006-302925 (especially, claims 1 and 5, paragraph 0050, FIG. 5) discloses a fabrication method of an organic transistor, in which a PEDOT/PSS gate electrode film is formed on a substrate, a polyvinylphenol gate insulating film is formed on the gate electrode film, a PEDOT organic semiconductor material film is formed on the gate insulating film, and a PEDOT/PSS source electrode film and a drain electrode film are formed on the organic semiconductor material film.
However, in order to insulate an organic semiconductor material film and a gate electrode film, after the formation of the gate electrode film, a gate insulating film forming process through a spin coating method is required. Thus, it was difficult to sufficiently simplify fabrication processes.